1. Field of the Invention
This invention relates to a novel lifting and material handling apparatus. More specifically, this invention relates to such apparatus which can be adapted to either semi-automatic, automatic or remote control operation.
2. Statement of the Prior Art
The prior art teaches many lifting and material handling apparatus, for example sheet lifting apparatus, as shown in U.S.A. Pat. Nos. 2,375,747, Brown, May 15, 1945; 2,732,248, Jaeger, Jan. 24, 1956; 3,044,819, Pierre, July 17, 1962; 3,198,568, Mindrum, Aug. 3, 1965; 3,854,766, Dec. 17, 1974, Jordan and 3,796,332, Kawamura, Mar. 12, 1974. Basically, the apparatus of the prior art consist of three types: The first is the low headroom type which uses a rack and pinion drive to close the grasping legs thereof. This type does not have a very powerful gripping action and can therefore be unsafe.
The second and third types use the tong principle and consist of the parallelogram type and the adjustable angle type.
The adjustable angle type has the disadvantage of requiring frequent adjustment of angles, and if the operator is careless, and does not correctly adjust the angles, safety is compromised.
Both the parallelogram type and the adjustable angle type require a hand wheel operated mechanism to open and close the legs. This mechanism requires a high ratio gear box, mechanical load brake and various linkages etc. All this apparatus is very costly and increases the dead weight of the unit. Furthermore, the operation of the hand wheel is time consuming and requires a good deal of physical effort.